Preparation And Electrocatalytic Water Splitting Performance Of Transition Metal Phosphide Nanoarray Electrode

The hydrogen economy,in which electricity is generated from renewable sources,splitting water into hydrogen and oxygen,and then further utilizing clean hydrogen fuels,has become a very promising alternative to the current hydrocarbon economy.However,the current process of hydrogen production by electrolysis of water suffers from low energy utilization efficiency and high cost of hydrogen production.Therefore,there is an urgent need to develop electrochemical efficiency enhancement technologies for water electrolysis.The electrochemical efficiency of electrolysis is closely related to the performance of catalysts used for hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）in electrolysis process.Therefore,this thesis focuses on transition metal phosphide nanoarray catalysts with bifunctional catalytic activity of HER/OER,and the main research contents and conclusions obtained are as follows:（1）CoP/Ni₂P/MoO_x composite catalyst was prepared by two-step hydrothermal-low temperature phosphating method with nickel foam as the substrate.By adjusting the amount of Ni（NO₃）₂·6H₂O and Na₂MoO₄·2H₂O in secondary hydrothermal addition,as well as the amount of sodium hypophosphate during phosphating,the CoP nanowire-Ni₂P/MoO_xnanosheet core-shell array structure material with larger specific surface area was obtained.The electrochemical test results showed that CoP/Ni₂P/MoO_x-P200 exhibited good HER and OER catalytic activity in 1 M KOH electrolyte,with overpotentials of 69.4 m V and 224.9 m V at a current density of 10 m A cm-2,respectively.The corresponding tafel slope are 58.23 m V dec-1 and 47.9 m V dec-1.When CoP/Ni₂P/MoO_x-P200were used as both anode and cathode,the total hydrolytic potential at 10m A cm-2 was 1.545 V.After 20 h of chronopotential testing,the overpotential of HER and OER did not increase,and the morphology and phase of the catalyst did not change,showing good stability.The excellent catalytic activity of CoP/Ni₂P/MoO_x-P200 is mainly attributed to more defects caused by low crystallinity and more active sites exposed by the core-shell array structure of nanowire-nanosheet.（2）A transition metal phosphide nanoarray material（Ni₂P/Fe₂P/MoO_x）with bifunctional catalytic activity was successfully synthesized on nickel foam by a hydrothermal-ion-exchange-phosphating method.The Ni₂P/Fe₂P/MoO_x-4.5 h catalyst showed excellent HER and OER catalytic performance in alkaline system,requiring only 73.1 and 215.2 m V low overpotential to reach the current density of 10 m A cm-2.When it was assembled into two electrodes for water electrolysis performance test,the overall water decomposition current density of 10 m A cm-2 could be obtained only at 1.526 V potential.After 100 h of constant current test,the potential basically did not change,showing super strong stability.Its excellent catalytic performance of water decomposition is mainly attributed to the following aspects:The presence of Fe in the OER process changes the electronic structure of Ni,forming highly active Fe Ni oxyhydroxide and optimizing the chemisorption of oxygen-containing intermediates;metal phosphides serves as the active site for catalyzing HER and provides a conductive scaffold for Fe Ni oxyhydroxide formed on the surface during OER to ensure rapid charge transfer;the nanowire array structure facilitates the contact between the material and the electrolyte and the exposure of the active sites.